Add pretty-printing to unittest and more thoroughly print values.

pkg/unittest/lib/src/numeric_matchers.dart

Index: pkg/unittest/lib/src/numeric_matchers.dart
diff --git a/pkg/unittest/lib/src/numeric_matchers.dart b/pkg/unittest/lib/src/numeric_matchers.dart
index e5dd7ef9d57cae5e586b6bfab39a8812f987c6f7..84afb49c2fd70b5071b2c8206242b06070e38762 100644
--- a/pkg/unittest/lib/src/numeric_matchers.dart
+++ b/pkg/unittest/lib/src/numeric_matchers.dart
@@ -150,14 +150,11 @@ class _IsCloseTo extends BaseMatcher {
   Description describeMismatch(item, Description mismatchDescription,
                                MatchState matchState, bool verbose) {
     if (item is !num) {
-      return mismatchDescription.
-          addDescriptionOf(item).
-          add(' not numeric');
+      return mismatchDescription.add(' not numeric');
     } else {
       var diff = item - _value;
       if (diff < 0) diff = -diff;
       return mismatchDescription.
-          addDescriptionOf(item).
           add(' differed by ').
           addDescriptionOf(diff);
     }